Taxes, pensions, and the delicate task of compromise; Can Reagan meet Congress halfway, keep momentum?

On two major issues -- tax cuts and social security --President Reagan must try to find compromise without tarnishing his image of consistency and control. "A mistake" is the way Rep. James R. Jones (D) of Oklahoma, chairman of the House Budget Committee, describes Mr. Reagan's proposals for changing the social security system.

The President "may have been somewhat innocent politically," says Rep. Barber B. Conable Jr. (R) of New York, and "not have realized the storm he would create."

Leaders of both parties rule out any abrupt reduction of benefits for early retirees, a proposal that is the centerpiece of Reagan's plan.

"I am unwilling to do dirt to 61-year-olds," said Mr. Conable, "without further study" of alternative methods of improving the system.

Compromise on how to rescue the financially sagging social security system seems certain, although the shape of the rescue remains to be worked out between Congress and the White House.

On taxes, Mr. Jones told reporters at breakfast, the President may have his way "if he devotes as effective lobbying [for his tax-cut plan] as he did on the budget."

This, despite widespread concern among many Democrats and some Republicans that Reagan's program of a 30 percent across-the-board income tax cut over three years might prove inflationary.

The question is: If the President has to compromise on one or both issues, will he lose the momentum gained through his smashing budget triumph in Congress?

The fiscal 1982 budget soon to emerge from Congress bears the hallmark of Reagan, won through solid Republican support and the defection of many House Democrats to the President's side.

"A compromise [on taxes or social security] would not necessarily stall that momentum," said Jones, because Americans hunger for a strong president and they perceive that in Reagan.

"His momentum," the House budget chairman said, "might be stalled more by a perception that he was unwilling to compromise."

Conable, ranking Republican member on the tax-writing House Ways and Means Committee, sounds a note of caution: "Will the tax program appear to be his [ Reagan's] package or something else? A one-year cut might look like a defeat for the President. So multiyear becomes a litmus test."

The President, in short, wants a multiyear commitment on taxes from Congress, although this might end up being two years, instead of three.

"No tax bill," Conable says, "is feasible without it bearing the strong image of Reagan's authorship."

Currently the stock, bond, and financial markets appear to be turning thumbs down on Reagan's economic program, with money managers acting as though they expect high inflation to continue.

This concern springs from several sources:

* Fear that the Reagan program may enlarge the budget deficit, which would impel the Federal Reserve Board to tighten credit.

* A parallel concern that government spending cannot be controlled until the White House and Congress are willing to change the indexing formula that now boosts social security and other costs by billions of dollars yearly.

* Doubt that the Fed is able to control the growth of the nation's money supply, a prime cause of inflation.

If the markets persist in these views, says Jones -- or if there is a public backlash against Reagan's tax-cut program -- the White House may shift ground on its own .